Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX
pubs.acs.org/JPCC
Ice II-like Monolayer Ice Grown on Graphite Surface Ya-Ru Wang,† Ji-Yu Xu,‡ Chao-Ke Ma,† Ming-Xia Shi,† Yu-Bing Tu,§ Kai Sun,† S. Meng,*,‡ and Jun-Zhong Wang*,† †
School of Physical Science and Technology, Southwest University, Chongqing 400715, China Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China § Department of Physics, Nanchang Normal University, Nanchang 330032, China
Downloaded via NOTTINGHAM TRENT UNIV on August 14, 2019 at 08:20:21 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
‡
ABSTRACT: Water on solid surfaces is essential for a wide range of scientific and technological processes. Previous studies reveal that water molecules on metal surfaces usually form layered structures with a honeycomb hydrogen-bond network, similar to the basal plane of hexagonal ice Ih. Here we report a new type of monolayer ice grown on graphite surface at low temperature with subsequent annealing. High-resolution STM images reveal that the monolayer ice is composed of cyclic water hexamers without sharing edges. Moreover, the monolayer ice exhibits multiple orientations relative to the graphite lattices, resulting in various moiré patterns. First-principles calculations reveal that the moiré superstructures contain both tilted and planar water hexamers, corresponding to the horseshoe-like and flat water rings observed in the STM images. All water molecules within the monolayer are saturated by four hydrogen bonds, and the strong intralayer bonding gives rise to a high stability of the monolayer ice.
I. INTRODUCTION Water is very universal in nature and has great importance in biology and in materials sciences. The interactions of water with solid surfaces are critical in various scientific and technological processes because the interfacial water structures determine the wetting properties.1−9 On metals surfaces, twodimensional ice structures have been widely investigated by low temperature experiments and were previously interpreted in terms of the ice-like bilayer model, where the water molecules adopt the puckered structure like the basal plane of hexagonal ice Ih.3,5,10−13 However, recent experimental and theoretical studies demonstrate that some kinds of disorder or distortion existed in the two-dimensional (2D) ices due to the competition between water−water and water−solid interactions. For example, scanning tunneling microscopy (STM) studies reveal that, on Pd(111), Pt(111), and Ni(111), the monolayer ice is composed of rotated hexagonal rings bridged by pentagonal and heptagonal rings.14−20 On the more reactive Ru(0001) surface, water molecules dissociate into hydroxyls and hydrogen.21,22 For the monolayer ice grown on insulating NaCl films, a regular array of Bjerrum D defects was found.23 Compared with the extensive studies of water on metal or insulating surfaces, the ice structures formed on semimetal surfaces, such as graphite or graphene, have received less attention. Graphite or graphene is a good template for studying © XXXX American Chemical Society
the interfacial water structures because of the homogeneity and morphological flatness.24−26 In the past decades, there are have been some studies on the adsorption, desorption, wetting, and crystallization of water on graphite/graphene surfaces, using spectroscopic and diffraction techniques27−43 and molecular dynamics simulations (MDS).44−48 It was found that the structures of water overlayer are highly dependent on the deposition conditions and substrate temperature. With increasing temperature, the ice films can range from amorphous solid water (ASW), bilayer ice, ice Ih, to liquid water. A novel 2D ice consisting of two flat hexagonal sheets was found on the monolayer graphene grown on Pt(111), based on the analyses of low energy electron diffraction and ab initio molecular dynamic (MD) simulations.27 A novel square ice was observed in the hydrophobic nanoconfinement between two graphene sheets.49 Recently, we explored a technique of “low temperature deposition with subsequent annealing” to fabricate the ordered monolayer ice on graphite surface.50 In this Article, we report the details of the growth and structural features for the monolayer ice. High-resolution STM images demonstrate that Received: May 7, 2019 Revised: August 4, 2019 Published: August 5, 2019 A
DOI: 10.1021/acs.jpcc.9b04310 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C the monolayer ice is composed of tilted and flat water hexamers without sharing edges. Especially, we present a series of moiré patterns that appeared in the monolayer ice formed under different misorientation angles. Achiral and chiral Kagome lattices, as well as odd−even transition have been identified.
moiré patterns indicate that there exist lattice mismatch and misorientation between the lattices of ordered monolayer ice and graphite substrate. Considering the poor conductivity of disordered wetting layer, we used a high bias voltage (>3 V) and a small tunneling current (
